In recent years, the market of electric energy storage devices such as a photovoltaic power generating device, and an electric automotive vehicle, an emergency power source and the like is expanding, so that technical developments of a zero-energy house and a zero-energy building receive attention in which purchased electric power from an electric power system is made zero by means of an apparatus where those devices are combined. However, when a plurality of different electric energy storage devices is used in which they are multi-structured in parallel with one another, there exists a condition in which better efficiency is achieved when limits are imposed on the operating number of the electric energy storage devices and on their electric power sharing by responding to their charge-discharge electric-power than when all of the electric energy storage devices charges or discharges their electric power at the same ratios through their electric power sharing.
In Patent Document 1, a plurality of electric power converters each of which has the same electric-power capacity is used, and electric power corresponding to the highest efficiency of each of the electric power converters and rated electric power thereof are preferentially utilized, whereby increased efficiency is implemented. However, when a plurality of electric power converters each of which has different electric-power capacity is used, higher efficiency is achieved under a condition in which electric power is small when a plurality of electric power converters each of which has small electric-power capacity is used than when one piece of an electric power converter having large electric-power capacity is used; higher efficiency is achieved under a condition in which the electric power is large when an electric power converter having better efficiency is preferentially utilized from among the electric power converters; and so forth. Because the conditions differ for the sake of increased efficiency, there exists a condition in which such utilization in Patent Document 1 does not result in increased efficiency.